Study on compressive strength and thermal conductivity of interlayer reinforced and stiffened CFRP composites with CNT films

In recent years, the structure-function integrated carbon fiber reinforced plastic (CFRP) composites have attracted extensive attention, and the interlayer reinforcing and stiffening based on carbon nanotube (CNT) films with high strength, high modulus and high thermal conductivity provided an innovative idea. In this paper, the stretched CNT films (S-CNTF), epoxided CNT films (E-CNTF) and stretched-epoxided CNT films (S-E-CNTF) were prepared by wet stretching and epoxidation reaction based on pristine CNT films (P-CNTF), and used for interlayer reinforcing and stiffening CFRP composites (CFRP/S-CNTF, CFRP/E-CNTF and CFRP/S-E-CNTF), respectively. The physicochemical characteristics and tensile properties of CNT films were analyzed, and the effects of S-E-CNTF on longitudinal compressive strength and failure mechanism of composites were studied by combining Jumahat's combined model and experimental verification. Meanwhile, the in-plane thermal conductivity and corresponding mechanism of composites were discussed. In contrast with P-CNTF, the CNTs in S-E-CNTF present highly oriented bunching morphology and the surface chemical activity of S-E-CNTF is observably improved, so that the tensile strength and modulus of S-E-CNTF are enhanced to 116 MPa and 6.3 GPa, respectively. In comparison with CFRP, the in-plane shear modulus and interlaminar shear strength of CFRP/S-E-CNTF are increased by 28.3% and 34.2%, respectively, implying that the S-E-CNTF can effectively inhibit delamination and enhance resistance of shear deformation of CFRP. The model prediction also shows that the theoretically elastic and plastic compressive stress of CFRP/S-E-CNTF are increased by 30.7% and 32.3%, respectively, which is in accord with experimental values. Meanwhile, based on the three-dimensional thermal conductivity network constructed by S-E-CNTF in the interlaminar region of CFRP, the in-plane thermal conductivity of CFRP/S-E-CNTF is improved to 7.8 W/(m·K).